1. Field of Invention
The present invention relates to image signal processors and image signal processing methods for converting image signals in an interlace system into image signals in a progressive scan system.
2. Description of Related Art
Various types of image display devices, such as a liquid crystal projector, for receiving image signals supplied from electronic devices, e.g., a personal computer; and for displaying images are proposed. Concerning transmission systems for transmitting image signals handled by these image display devices, there are a progressive scan system and an interlace system. In the progressive scan system, image signals corresponding to all horizontal scanning lines constructing a single screen in a single frame are transmitted in order. In contrast, in the interlace system, a single frame is divided into two fields. In a first field (odd field), every other horizontal scanning line constructing a single screen is selected and image signals corresponding to the selected horizontal scanning lines are transmitted. In a subsequent field (even field), image signals corresponding to the remaining horizontal scanning lines are transmitted.
Of the image display devices including the liquid crystal projector, there is a type for converting, when image signals in the interlace system are supplied, the image signals into image signals in the progressive scan system, writing the image signals in a frame memory, and displaying the image signals.
Hitherto, an image signal processor with a structure shown in FIG. 8 has been used to perform conversion in such an image display device.
In FIG. 8, a field determining unit II determines whether a phase difference between a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync input subsequent to the vertical synchronization signal Vsync is within a predetermined value, thus determining that the field starting with the vertical synchronization signal Vsync is an odd field or an even field. An image signal input in the odd field is written in an odd field memory 13 via a switch 12. An image signal input in the even field is written in an even field memory 14 via the switch 12. The image signals corresponding to the horizontal scanning lines are alternately read from the odd field memory 13 and the even field memory 14, and are sequentially written in a frame memory 15. As a result, the image signals of a progressive scan image on a single screen are obtained in the frame memory 15.
In recent personal computers or the like, the number of horizontal scanning lines and the pixel density can be arbitrarily set, and the personal computer and the image display device may be connected by various transmission media. Therefore, it is not ensured that the vertical synchronization signal Vsync and the horizontal synchronization signal Hsync output from the personal computer are transmitted to the image display device while maintaining the phase difference. Under these circumstances, the phase difference between the vertical synchronization signal Vsync and the horizontal synchronization signal Hsync output from the personal computer is not constant. If the odd-even determination is performed based on the phase difference between the above vertical synchronization signal Vsync and the horizontal synchronization signal Hsync, the determination may be incorrect, and a normal progressive scan image cannot be obtained.
In view of the above-described circumstances, it is an object of the present invention to provide an image signal processor and an image signal processing method for arranging image signals in fields in a normal order and thereby constructing image signals of a progressive scan image, even when image signals in an interlace system are input, while a phase difference between a vertical synchronization signal and a horizontal synchronization signal is not constant.
An image signal processing method or an image signal processor according to a first invention associatively stores elapsed times from the input of a vertical synchronization signal to the input of horizontal synchronization signals and image signals subsequent to the horizontal synchronization signals in a storage device, and forms image signals of a progressive scan image by arranging the image signals stored in the storage device within two successive vertical scanning periods in an order of the elapsed times corresponding to the image signals.
Therefore, it is possible to obtain the image signals of the progressive scan image by arranging the image signals corresponding to horizontal scanning lines in display order even when a phase difference between the vertical synchronization signal and the horizontal synchronization signal is not constant.
According to a second invention, elapsed times from the input of a vertical synchronization signal to the input of horizontal synchronization signals and image signals subsequent to the horizontal synchronization signals are stored in a storage device. Based on the elapsed times stored in the storage device within two successive vertical scanning periods, an order of reading image signals within the vertical scanning periods from the storage device is determined. The image signals corresponding to horizontal scanning lines within the vertical scanning periods are alternately read from the storage device in that order, thus forming image signals of a progressive scan image.
In this case, it is not necessary to sort all image signals in accordance with timer values. This reduces arithmetic processing and increases the processing speed.
According to the above first or second invention, if a difference between the elapsed times within the two successive vertical scanning periods is within a predetermined range, the input image signals corresponding to the horizontal scanning lines can be output in the order as they are input.
Accordingly, it is possible to perform processing when image signals not only in an interlace system but also in a progressive scan system are input.
In each invention, the storage device is not necessarily a single memory. As long as the elapsed times and the image signals are associatively stored, the two can be stored in separate memories. In this case, the memory storing the elapsed times and the memory storing the image signals form the xe2x80x9cstorage devicexe2x80x9d in the present invention.